In this article, the effects of different diverging-converging pore geometries were investigated, and the microscale fluid flow and effective hydraulic properties from these pores were compared with that of a pipe from viscous to inertial laminar flow regimes. The flow fields are obtained using computational fluid dynamics, and the comparative analysis is based on a new dimensionless hydraulic shape factor β, which is the "specific surface" scaled by the length of pores. Results from all diverging-converging pores show an inverse pattern in velocity and vorticity distributions relative to the pipe flow. The hydraulic conductivity K of all pores is dependent on and can be predicted from β with a power function with an exponent of 3/2. The differences in K are due to the differences in distribution of local friction drag on the pore walls. At Reynolds number (Re) ∼ 0 flows, viscous eddies are found to exist almost in all pores in different sizes, but not in the pipe. Eddies grow when Re →1 and leads to the failure of Darcy's law. During non-Darcy or Forchheimer flows, the apparent hydraulic conductivity Ka decreases due to the growth of eddies, which constricts the bulk flow region. At Re > 1, the rate of decrease in Ka increases, and at Re >> 1, it decreases to where the change in Ka ≈ 0, and flows once again exhibits a Darcy-type relationship. The degree of nonlinearity during non-Darcy flow decreases for pores with increasing β. The nonlinear flow behavior becomes weaker as β increases to its maximum value in the pipe, which shows no nonlinearity in the flow; in essence, Darcy's law stays valid in the pipe at all laminar flow conditions. The diverging-converging geometry in pores plays a critical role in modifying the intrapore fluid flow, implying that this property should be incorporated in effective larger-scale models, e.g., pore-network models.
K. Chaudhary et al., "Pore Geometry Effects on Intrapore Viscous to Inertial Flows and on Effective Hydraulic Parameters," Water Resources Research, vol. 49, no. 2, pp. 1149-1162, American Geophysical Union (AGU), Feb 2013.
The definitive version is available at https://doi.org/10.1002/wrcr.20099
Civil, Architectural and Environmental Engineering
Keywords and Phrases
Comparative analysis; Degree of non-linearity; Hydraulic parameters; Hydraulic properties; Laminar flow conditions; Laminar flow regimes; Pore-network models; Vorticity distribution; Computational fluid dynamics; Flow fields; Groundwater flow; Hydraulic conductivity; Laminar flow; Reynolds number; Seepage; Geometry; Darcy law; Fluid flow; Nonlinearity; Pore space
International Standard Serial Number (ISSN)
Article - Journal
© 2013 American Geophysical Union (AGU), All rights reserved.
01 Feb 2013